Polyolefin composition resistant to hot alkaline solutions

ABSTRACT

A composition characterized by resistance to hot alkaline solutions comprising a polymer formed from monomers including propylene, a stabilizer system including tetrakis (methylene 3(3&#39;&#39;,5&#39;&#39;-di-t-butyl-4&#39;&#39;-hydroxyphenyl) propionate) methane and a tin maleate.

United States Patent 1191 McInerney 14 1 Apr. 15, 1975 POLYOLEFINCOMPOSITION RESISTANT TO HOT ALKALINE SOLUTIONS [75] Inventor: Edward J.Mclnerney, Louisville,

[73] Assignee: General Electric Company, New

York, NY.

[22] Filed: Nov. 12, 1973 21 Appl. No.: 414,915

[52] US. Cl ..260/897 A; 260/4575 T; 260/45.85 B

[51] Int. Cl. C08f 45/62 [58] Field of Search 260/4575 K, 45.85 B, 897 APrimary ExaminerV. P. Hoke [57] ABSTRACT A composition characterized byresistance to hot alkaline solutions comprising a polymer formed frommonomers including propylene, a stabilizer system including tetrakis[methylene 3-(3,5-di-t-butyl-4- hydroxyphenyl) propionate] methane and atin maleate.

9 Claims, No Drawings POLYOLEFIN COMPOSITION RESISTANT TO HOT ALKALINESOLUTIONS BACKGROUND OF THE INVENTION The present invention relates to apropylene-polymer composition which is particularly characterized byresistance to discoloration or deterioration in a hot alkaline aqueousenvironment such as that existing in an automatic dishwasher.

The design environment for a dishwasher tub is direct exposure to 180F,pH 1 2 dishwasher detergent solution with spot temperatures exceeding180F during the drying cycle. Because of these conditions, the usual tubmaterials have been porcelain enamel on steel, vinyl plastisol on steel,and stainless steel. Polypropylene compounds have been used in overseasdishwashers. However, the usual polypropylene compounds, including thosecontaining various stabilizer combinations or systems used or proposedfor imparting heat, light or strength stability to polypropylene resins,do not meet 7 the high United States reliability requirements fordishwasher tubs. In fact, as disclosed for example in US pat. No.3,409,587-Mills, the industry has experienced great difficulty inachieving the stabilization of polypropylene compositions for variousapplications and it is impossible to predict the combined effect of aplurality of stabilizers from their effects individually. Specifically,the Mills patent teaches that a fourcomponent stabilizer systemcomprising an organic phosphite such as dioctyl phosphite, a thioestersuch as dilaurylthiodipropionate, and two alkylphenol antioxidants suchas 1,1 ,3-tris(2-methyl-4-hydroxy-5-tertbutylphenyl)butane and tetrakis[3-(3,5-ditert-butyl-4- hydroxyphenyl)propeonyloxymethyl] methane is asuperior polypropylene stabilizer system for improving resistance todiscoloration and embrittlement upon exposure to air and light at normaland high temperatures.

Other prior art patents concerned with the polypropylene stabilizationproblems include US. pat. No. 3,310,509-Fukumoto et al. which teachesthat in the production of dyeable polyolefin composition containing atransition metal compound to promote dyeability, heat discoloration canbe prevented by incorporating a tin compound along with the transitionmetal compound, and photostability can be imparted by the furtheraddition of an alkylphenol type antioxidant.

US Pat. No. 3,285,855-Dexter is also concerned with this problem andcontains a rather comprehensive list of alkylphenol compounds suitablefor stabilizing organic materials, such as polypropylene resins, subjectto oxidative deterioration or heat or light deterioration.

SUMMARY OF THE INVENTION It is a primary object of the present inventionto provide a polypropylene composition containing a stabilizer systemparticularly adapted to withstand, without significant strength or colordeterioration, the rather unique and drastic environmental conditionsfound in a dishwasher.

In accordance with the presently preferred embodiment of the invention,this objective is obtained by providing a polypropylene compositionessentially containing as the primary alkylphenol antioxidant andthermal stabilizer, tetrakis [methylene3-(3',5-di-tertbutyl-4'-hydroxyphenyl) propionate] methane along withselected secondary antioxidants and stabilizers plus an effective amountof a tin maleate, specifically di-n-butyl tin maleate as a colorstabilizer.

The presently preferred formulation in which all additives are given asparts by weight is given in the following table:

At least one and preferably a mixture of alkyl or aryl thio diproionules are used. It distearyl thin dipropionate is utilized alone, theamount utilized will he not greater than 0.6 parts. It dilauryl thiodipropionate is utilized alone. the amount utilized will be not greaterthan 1.0 part.

The poly(propylene-ethylene) copolymer has an isotactic polypropylenecenter segment and contains approximately 1 to 6 percent ethylene byweight. Similar isotactic polypropylene homopolymers which may bemodified as known with ethylene propylene rubber or ethylene propylenediene modified rubber or as ternary blends of these rubbers with highdensity polyethylene, such as are disclosed in US. Pat. No.3,562,790Coover et al., may be used. Calcium stearate is a commonly usedlubricant. The bisphenol-A- epoxy is commonly used as a crazingresistant additive while the phosphite has been generally used as aprocessing stabilizer to prevent discoloration during processing ofpolypropylene compounds.

For a clearer understanding of the invention, the following examples aregiven:

EXAMPLE I Q pprs 'JILIIGOLJI parts Propylene-ethylene copolymer alcfiller TiO. pigment Primary antioxidant (as indicated) Distearyl thiodipropionate Calcium stearate Distearyl pentaerythritol diphosphiteMolded samples in the form of sheets 0.060 inch in thickness containingthe different primary antioxidants as listed in Table II were heated ina forced air convection oven to C to determine their resistance tovisual craze before and after being subjected to the indicated cycles(DW cycles) of exposure to a dishwasher environment, each cycleinvolving exposure to F water solution of 0.35% of the dishwasherdetergent, commercially available under the name *Cascade" and a dryingcycle of one hour at about 180F. The figures given in the table are theaverage of the tests on two or three samples of each composition.

TABLE 11 Days to Visual Craze Following Exposure Nominal D/W The primaryantioxidants employed in preparing the compositions for the tests setforth in TABLE 11 are listed and where possible identified by chemicalname.

EXAMPLE 2 To determine the effect of additive interactions on crazeresistance and color stability, polypropylene compounds were preparedhaving the compositions described in TABLE 111. All compositions areexpressed as parts by weight.

TABLE 111 C ompos- Phosition* Calcium phite BPA Epoxy Tin Number DSTDPStearatc (a) Resin maleate *COMMON TO ALL MATERIALS 100 partspropylene-ethylene copolymer 25 parts Talc I 2.5 parts TiO Compohmu"Punk) Am'oxldmt 0.5 part Ciba-Geigy lrganox 1010 tetrakis [methylene3-3' ,5 '-di-t-butyl-4-hydroxyphenyl )propionate ]me- 1708 tetrakis[methylene 25 m Y y yp y (a) distearyl pentaerythritol diphosphiteprop1onate] methane 1710'di-n-octadecyl-2-(3'5'-tli-tert-butyl-4'-hydroxyphenylladi ate Theellowin tendenc of these com ositions was 1711 d4 '1 '1 3'5'd' b 14' ggf 'gg g fi n j determined under the 1nd1cated test conditions employ-1712 zinc dicyclohexyl dithio phosphinate ing a color difference meterper American Society of 22 33:;EZHJiiiiififif' Testing and MaterialsStandard D1925. Data are re- 1714 l.l,3-tris(5tert-butyl-4-hydroxy-Z-methylphenyl) Ported as the change in yellownessj q following 771 posure [i.e., Y1 (exposed) Y1 (1n1t1al)].

lrinlflhylaAbm31'5Idi ten butyl 4ghydroxy The results of these tests areset forth in TABLE IV.

benzyl )benzene 35 1548 Thin diethylenebis-(3.5-di-tert-butyl-4-hydroxy)hydrocinnamate TABLE IV 1549 Octadecyl3-( 3 ,5 di-te rt-butyl-4 '-hydroxyphenol )propionate Yellowness lndexChange Following Exposure 1550 0,0 D/Wdi-N-octadecyl-3,5-di-tert-butyl-4-hydroxybenzyl Cycles 750 1500 2160750 1500 2160 phosphonate 40 Compos- 1558 1,3,5-tris(2.6-di-tert-hutyl-4-methylene ition phcnohisocyanurate Number 180F 150F1738 12.7 17.4 18.6 13.7 10.8 18.2 1739 11.9 25.2 32.4 11.9 12.3 22.1From the results set forth in TABLE [1, 1t W111 be seen 1740 13.7 22.225.0 13.7 13.9 that composition 1708 containing the primary antioxi-1Z1; 1 -8 $3 3-2 3-: :2? dant employed in the practice of the presentinvention H45 1:; is the only composition exhibiting good craze resis-1746 1812 21.7 29.8 29.9 14.9 19.5 27.9 tancc after substantlal exposureto a common alkaline dishwasher environment and a craze resistance whichdeclined the least as a result of such exposure. Crazing is a measure ofthe useful life of a plastic composition in the drastic high temperatureaqueous pH 10 to 12 detergent environment ofa dishwasher. However, ofall of the compositions listed in TABLE I1, composition 1708 also showedthe greatest change in color, a significant yellowing, after exposuretothe dishwasher environment, indicating also that the yellowing wascaused by the particular primary antioxidant characterizing composition1708.

The present invention is based on the discovery that the yellowingcaused by this specific primary antioxidant can be controlledsubstantially by the addition of a tin maleate, specifically di-n-butyltin maleate. The test results on various compositions as set forth inthe following examples show that while the tin maleate addition causes aslight, but acceptable, drop in oxidative stability, it markedlyimproves the color stability.

From these test results, it will be seen that variations in differentadditives had no significant effect except for the addition of the tinmaleate (compositions 1745 and 1746) which materially improvedresistance to yellowing.

For comparison, the craze resistance of these compositions are given inTABLE V.

TABLE V-Continued TABLE VIII-Continued Days To Visual Craze FollowingExposure The effect of the tin maleate addition was further proven bythe results of tests on additional compositions which along with thetest results on certain of the compositions previously described are setforth in TA- BELS VI and VII while the compositions are described inTABLE VIII.

TABLE VI Days To Visual Craze Following Exposure D/W Cycles 0 750 1500Composition Days To Craze at 150C (0.060 inch thick) Number 180F 150FThe following TABLE VII gives the yellowing test results.

The ingredients in the various systems listed in TA BLES VI and VII arelisted in the following TABLE VIII.

TABLE VIII Composition Number 1741 System V nothing 1745 System V 0.20phr di-n-butyl tin maleate 1743 System VII nothing 1746 System VII 0.20phr di-n-butyl tin maleate 1744 System VIII nothing 1747 System VIII0.20 phr di-n-butyl tin maleate 1760 System IX nothing 1756 System IX0.20 phr di-n-butyl tin maleate BASIC COMPOSITIONS:

SYSTEMS V VII VIII IX Propylene-ethylene copolymer 100 100 100 100 Talc(filler) 25 25 25 TiO 2.5 2.5 2.5 2.5

Composition Number Tetrakis[methylene-3-(3',5-di-tertbutyl-4'-hydroxyphenyl) propionate] methaneDistearyl thio dipropionate 0. Calcium stearate 0.

Disteuryl Pentaerythritol diphosphite Bisphenol A epoxy resinN.N'-di-acetyladipic acid dihydrazide 1.3 .5-tris( 2.6-di-tert-butyl 4-methylene phenol) isocyanurate From the test results of TABLE VII itwill be seen that l,3,5-tris(2,6-di-tert-butyl-4-methylene phenol)isocyanurate (Composition 1756) may be advantageously substituted forpart of the Irganox 1010. However, the primary stabilizer tetrakis[methylene 3- (3',5-di-t-butyl-4-hydroxyphenyl) propionate] methane isessential for the mechanical life of the composition under dishwasherconditions and this antioxidant appears to be unique in this respect. Itis also presently conceived that the anti-yellowing contribution of thetin maleate may be obtained by equivalent organo tin maleates andparticularly by similar alkyl derivatives such as diisobutyl tin maleateand di-n-oetyl tin maleate. It is further contemplated that changes canalso be made in the remaining ingredients including the secondaryantioxidants. Accordingly, it is intended by the appended claims tocover all such compositions as fall within the true spirit and scope ofthe invention.

I claim:

1. A composition having improved resistance to aging and discolorationin a high-temperature aqueous alkaline environment comprising apolymeric resinous material, a major portion of which is a moietyselected from propylene homopolymer, propylene-ethylene copolymer andpropylene and ethylene polymer blends; and a stabilizer systemcomprising tetrakis (methylene3-(3',5-di-t-butyl-4'-hydroxyphenyl)propionate) methane as anantioxidant and a dialkyl tin maleate as its principal constituents,said tetrakis methane constituent being present in an amount in therange of between about 0.20 and 1.50 percent by weight and said tinmaleate being present in an amount in the range of between about 0.05and 0.25 percent by weight.

2. A composition according to claim 1 also including a secondantioxidant.

3. A composition according to claim 1 in which said di-alkyl tin maleateis di-n-butyl tin maleate.

4. A composition according to claim 1 in which said secondaryantioxidant is distearyl thiodipropionate.

5. The composition of claim 1 wherein the alkyl groups of said dialkyltin maleate contain from one to eight carbon atoms.

6. The composition of claim 1 wherein said polymeric resinous materialis a homopolymer of polypropylene modified with a rubber compoundselected from ethylenepropylene rubber, ethylene propylene dienemodified rubber, and combinations thereof.

7. A composition particularly characterized by its resistance to hotalkaline environment comprising a copolymer of propylene and ethyleneand a stabilizer system consisting of tetrakis (methylene3(3',5-di-tbutyl-4'-hydroxyphenyl)propionate) methane, disteabeingpresent in an amount in the range of between about 0.05 and 0.25 percentby weight.

8. A composition according to claim 7 in which said tin maleate isdi-n-butyl tin maleate.

9. The composition of claim 6 wherein said propylene ethylene copolymerincludes an isotactic polypropylene center segment and contains aboutone to about six percent ethylene by weight.

1. A COMPOSITION HAVING IMPROVED RESISTANCE TO AGING AND DISCOLORATIONIN A HIGH-TEMPERATURE AQUEOUS ALKALINE ENVIRONMENT COMPRISING APOLYMERIC RESINOUS MATERIAL, A MAJOR PORTION OF WHICH IS A MOIETYSELECTED FROM PROPYLENE HOMOPOLYMER, PROPYLENE-ETHYLENE COPOLYMER ANDPROPYLENE AND ETHYLENE POLYMER BLENDS; AND A STABILIZER SYSTEMCOMPRISING TETRAKIS (METHYLENE3-(3'',5''-DI-T-BUTYL-4''HYDROXYPHENYL)PROPIONATE) METHANE AS ANANTIOXIDANT AND A DIALKYL TIN MALEATE AS ITS PRINCIPAL CONSTITUENTS,SAID TETRAKIS METHANE CONSTITUENT BEING PRESENT IN AN AMOUNT IN THERANGE OF BETWEEN ABOUT 0.20 AND 1.50 PERCENT BY WEIGHT AND SAID TINMALEATE BEING PRESENT IN AN AMOUNT IN THE RANGE OF BETWEEN ABOUT 0.05AND 0.25 PERCENT BY WEIGHT.
 2. A composition according to claim 1 alsoincluding a second antioxidant.
 3. A composition according to claim 1 inwhich said di-alkyl tin maleate is di-n-butyl tin maleate.
 4. Acomposition according to claim 1 in which said secondary antioxidant isdistearyl thiodipropionate.
 5. The composition of claim 1 wherein thealkyl groups of said dialkyl tin maleate contain from one to eightcarbon atoms.
 6. The composition of claim 1 wherein said polymericresinous material is a homopolymer of polypropylene modified with arubber compound selected from ethylenepropylene rubber, ethylenepropylene diene modified rubber, and combinations thereof.
 7. Acomposition particularly characterized by its resistance to hot alkalineenvironment comprising a copolymer of propylene and ethylene and astabilizer system consisting of tetrakis (methylene3(3'',5''-di-t-butyl-4''-hydroxyphenyl)propionate) methane, distearylthiodipropionate and dilauryl thiodipropionate and a dialkyl tin maleateas a color stabilizer, said tetrakis methane constituent being presentin an amount in the range of between about 0.20 and 1.50 percent byweight, said distearyl thiodipropionate being present in an amount inthe range of between about 0.1 and 0.6 percent by weight, said dilaurylthiodipropionate being present in an amount in the range of betweenabout 0.1 and 1.0 percent by weight and said dialkyl tin maleate beingpresent in an amount in the range of between about 0.05 and 0.25 percentby weight.
 8. A composition according to claim 7 in which sAid tinmaleate is di-n-butyl tin maleate.
 9. The composition of claim 6 whereinsaid propylene ethylene copolymer includes an isotactic polypropylenecenter segment and contains about one to about six percent ethylene byweight.